An improved map of the Galactic Faraday sky

TL;DR

This paper presents an improved all-sky map of Galactic Faraday rotation, utilizing extensive data and advanced algorithms to enhance accuracy and provide new insights into the Galactic magnetic field structure.

Contribution

It introduces a novel map-making algorithm that accounts for uncertainties and identifies rotation angle offsets, resulting in a more accurate and publicly available Galactic Faraday map.

Findings

Power law behavior with index -2.14 in the angular power spectrum

Map accounts for uncertainties and offsets in rotation angles

Results align with a 3D Fourier power spectrum of the underlying field

Abstract

We aim to summarize the current state of knowledge regarding Galactic Faraday rotation in an all-sky map of the Galactic Faraday depth. For this we have assembled the most extensive catalog of Faraday rotation data of compact extragalactic polarized radio sources to date. In the map making procedure we use a recently developed algorithm that reconstructs the map and the power spectrum of a statistically isotropic and homogeneous field while taking into account uncertainties in the noise statistics. This procedure is able to identify some rotation angles that are offset by an integer multiple of pi. The resulting map can be seen as an improved version of earlier such maps and is made publicly available, along with a map of its uncertainty. For the angular power spectrum we find a power law behavior with a power law index of -2.14 for a Faraday sky where an overall variance profile as a function of Galactic latitude has been removed, in agreement with earlier work. We show that this is in accordance with a 3D Fourier power spectrum P(k) proportional to k^-2.14 of the underlying field n_e times B_r under simplifying geometrical and statistical assumptions.